The present invention relates generally to a fluid seal apparatus. More particularly, the present invention relates to a sliding seal arrangement that provides linear and rotational mobility and flexibility in multiple degrees-of-freedom.
Mechanical seals, including liquid seals, gas seals, pressure seals, and vacuum seals, are widely used in a variety of applications. Materials such as metals, plastics, foams, and elastomers are commonly used to provide a sealing relationship between surfaces of two or more bodies by filling gaps or bridging voids interposing between these surfaces. Fluid seal configurations include, for example, flexible o-rings or gaskets, which are typically deformed under compression to provide an impermeable barrier between solid surfaces of spaced-apart bodies. Isolation of high-pressure fluids within a confinement structure, maintenance of a vacuum, separation of dissimilar fluids, and prevention of leakage and contamination are but a few applications for fluid seal apparatuses.
In addition, many seals are used to provide a controlled environment to equipment components or process workpieces within an enclosed chamber, isolating them from conditions exterior the enclosure. For example, seals may be used to prevent air and/or other gases from leaking into an enclosure to shield workpieces within the chamber from chemical or physical interaction with these gases. Numerous novel approaches and improvements to fluid seals have been offered.
An application wherein it is advantageous to present an effective fluid seal that provides both mobility and flexibility between the sealed bodies and damping of vibrational force across the seal is the lithography processing steps of semiconductor integrated circuit (IC) manufacture. Conventional lithography processes, for example, photolithography processes, include optical lithography systems and electron beam projection systems
Current IC manufacturing practices use lithography photomasks (reticles) to apply various patterns to a photosensitized semiconductor wafer used to create the ICs. Reticles are typically high-precision plates that contain a pattern of extremely small images of the various components of an electronic circuit. A reticle is used as a master to transfer a plurality of the circuit pattern onto a photosensitized wafer. Current state-of-the-art lithographic system often must position an ultra-fine image to within 15 nanometers. Current circuit architectures often have conductor linewidths as narrow as 30 nanometers. Accordingly, lithography processing equipment requires advanced precision optical and mechanical systems and even higher precision systems will be required in the future, as still smaller images become common.
Lithographic exposure apparatuses are used to project images from the reticle onto the photosensitized wafer during semiconductor processing. A typical exposure apparatus includes a base frame having a lower enclosure that contains a wafer stage for holding a semiconductor wafer workpiece. The base frame also supports an optical device that holds a reticle stage and is arranged to project the images from a reticle carried by the reticle stage onto the wafer workpiece. The base frame typically supports the optical device through a vibration isolation system designed to damp and isolate vibrations between components of exposure apparatus so that vibrations in one component are not transmitted to the other. This is deemed necessary because mechanical vibrations transmitted between components can adversely influence the accuracy of exposure apparatus. At the same time, it often is desirable to provide a controlled atmosphere (typically an inert atmosphere such as helium) in the region of the wafer enclosure. In order to reduce the region that must be most carefully controlled, it is often desirable to provide a seal between the exterior of the optical device (which might be in an air based atmosphere) and the lower enclosure (which may be in the controlled atmosphere). A potential problem with providing a seal between the optical device and the lower enclosure is that many if not most seal designs provide mechanical structures that may act to transmit vibrations between their associated components.
Therefore, there are continuing efforts to provide improved sealing devices that provide an effective fluid seal between two movable bodies and that further provides damping or isolation of vibrational force between the bodies.
To achieve the foregoing and other objects of the invention, a sliding seal system is described that provides a fluid seal between a pair of bodies while allowing low friction mobility in three degrees-of-freedom and low stiffness flexibility in three additional degrees-of-freedom between the bodies. Mobility is provided in one rotational and two linear directions ("THgr"Z, X, Y) while flexibility is provided in one linear and two rotational directions (Z, "THgr"X, "THgr"Y). 
In one embodiment, the sliding seal system includes a support member having a working surface arranged to provide a seal interface with a sealing surface on the first body. A flexible membrane is attached to the support member and coupled to the second body. A fluid supply system is provided to deliver a fluid to a region between the working surface of the support member and the sealing surface of the first body to provide buoyant flotation to the seal support member at the working surface. In a preferred embodiment, a fluid exhaust system is also provided to remove the fluid delivered by the fluid supply system.
In some embodiments, the fluid supply system includes fluid delivery passages and the fluid exhaust system includes fluid exhaust passages designed to remove fluid delivered through the fluid delivery passages. Such plumbing may be incorporated into the support member or the first body or into a combination of the two. The fluid delivery and exhaust systems may also include fluid distribution channels cut into either the working surface of the support member or the sealing surface of the first body for improving the distribution and/or collection of the fluid about the sealing region.
In some embodiments, the fluid supply system may include interior and exterior fluid delivery passages arranged to deliver different fluids to the sealing region. If a fluid exhaust system is provided, the fluid exhaust system may also include interior and exterior fluid exhaust passages. With this arrangement, the interior fluid exhaust passages are designed to remove fluid delivered through the interior fluid delivery passages and the exterior fluid exhaust passages are designed to remove fluid delivered through the exterior fluid delivery passages.
In some embodiments, the support member includes a top ring and a bottom ring and the flexible membrane is clamped between the top and bottom rings. With this arrangement, the fluidics can be at least partially incorporated into the bottom ring.
One particularly useful application of the described sliding seal system is in a photolithography system to provide a seal between an exposure apparatus and a wafer chamber. In specific embodiments, a lithography system having an illumination source, an optical system, a reticle stage arranged to retain a reticle and a working stage arranged to retain a workpiece (e.g. a wafer) is described. An enclosure having a sealing surface is provided that surrounds at least a portion of the working stage. A support member having a working surface is arranged to provide a seal interface with the sealing surface on the enclosure. A membrane is attached to the support member and coupled to the optical system to provide a seal for the workpiece (wafer) chamber. A fluid supply system delivers a fluid to a region between the working surface of the support member and the sealing surface of the enclosure to provide buoyant floatation to the support member at the working surface. With this arrangement, a sliding seal system is formed that provides a seal between the working surface of the enclosure and the optical system. The sliding seal arrangement may have any of the previously described configurations. Such lithography systems can be used to manufacture objects such as semiconductor wafers.
These and other features, aspects, and advantages of the present invention will become apparent upon reading the following detailed descriptions and studying the various figures of the drawings.